This invention pertains generally to the use of wide-area data networks to carry switched-circuit calls, and more particularly to an adjunct voice network system for routing calls across a wide area data network to connect a private voice network with a public switched telephone network.
A Private Branch Exchange (PBX) is an automatic telephone switching system that enables users within an organization to place calls to each other without going through the public switched telephone network (PSTN). Many large organizations require the deployment of numerous PBXs to form a private network that covers the organization.
Although an organization could connect each of its PBXs to the PSTN, and then rely on the PSTN in order to interconnect their PBXs, this approach is not always preferred. Leased tie lines between sites are generally expensive. Since many organizations maintain a Wide Area Network (WAN) for data communications between their various buildings and sites, it would be preferable if PBX-to-PBX communications could be routed across the WAN.
FIG. 1 shows an example of one configuration for connecting PBXs across a WAN. Four PBXs A, B, C, and D connect to WAN 16. Each PBX connects directly to one of switches 18, 19, 20, and 21, typically through one or more E1 or T1 trunks. Switches 18, 19, 20, and 21 communicate with each other using Frame Relay packets, ATM (Asynchronous Transfer Mode) cells, or another common WAN packet technology.
In order for the PBXs to communicate across WAN 16, a mesh of Permanent Virtual Circuits (PVCs) is set up between them. For instance PVC 22 connects PBXs A and B via a dedicated connection; likewise, PVC 24 connects PBXs C and D, PVC 26 connects PBXs A and C, and PVC 28 connects PBXs A and D. Although a Virtual Circuit only allocates a physical circuit when there is data to send, a PVC is similar to a dedicated private line because the connection is set up on a permanent basis.
A tradeoff exists between the number of PVCs that are set up between PBXs and the percentage of WAN bandwidth consumed. Although it may be practical to fully mesh the four PBXs of FIG. 1, with larger PBX networks partial meshing makes more sense in order to conserve bandwidth. Thus the PBXs of FIG. 1 are demonstrated as partially meshed. Although a caller on PBX A may directly contact a party attached to any of the PBXs, a caller on PBX B has no PVC directly available to a party attached to PBX C or PBX D.
With no direct PVC, it may still be possible for the caller to indirectly contact PBX C or D, by going through PBX A and using two tandem PVCs. But the use of tandem PBXs wastes PBX and WAN resources, and requires additional sophistication in the PBXs. It also generally precludes the use of a voice compression codec, or at least limits compression to one of the PVCs, as tandem encodings dramatically degrade sound quality.
With the system of FIG. 1, each PBX uses a separate trunk to connect to a central office in PSTN 40. Thus, when a user connected to PBX A desires to call a party reachable through PSTN 40, PBX A accesses a line to central office 30 to complete the call. Although in FIG. 1 each PBX is shown connected directly to a central office, in practice some PBXs may use a local tandem PBX to handle calls to the PSTN.
The networking approach shown in FIG. 1 has many disadvantages. As the private network size increases, scaling this model becomes increasingly complex, expensive, and wasteful. Each PBX must also provide a local trunk (or local tandem PBX route) to the PSTN if users of that PBX are to reach the outside world. Conversely, a PBX is required at any point where a connection to a PSTN central office is desired.
The embodiments described herein address these problems by adding one or more voice network appliances to an existing packet/cell based wide-area data network. Central office trunks and PBX trunks are tied to ports on WAN nodes, but PVCs are not established for the trunk bearer channels. The voice network appliances exchange signaling with PBXs and central offices tied to the wide-area data network, and dynamically establish voice and data connections directly between the PBXs and central offices as needed. Thus, to a PBX or a central office, the voice network appliance appears to be just another PBX. And yet, preferably, only signaling circuits are routed through the voice network appliance. The voice network appliance dynamically creates switched virtual circuits directly between the PBX and central office tie points to provide bearer channels for calls.
Each of the disclosed embodiments provide some or all of the following advantages. PBXs need not have local connections to the PSTN, and conversely, the PSTN may be tied to the wide-area network and interfaced with the private network without an intermediate PBX. This reduces hardware and trunk requirements significantly. A single port and signaling channel can serve many destinations, both private and public. Wide-area data network resources are conserved, since backbone trunk groups are eliminated. Since tandem PBXs are avoided, all calls can be compressed for transmission across the WAN. The system becomes highly scalable, since the only permanent circuits are the signaling circuits, which scale almost linearly as new ports are added. In embodiments with connections to several geographically diverse central offices, the voice network processor can also select an appropriate xe2x80x9cbreakoutxe2x80x9d point from the WAN to the PSTNxe2x80x94one that eliminates or reduces toll charges. And conversely, PSTN calling parties can reach anyone anywhere on the private network by calling a nearby central office number and xe2x80x9cbreaking inxe2x80x9d to the private network through the voice network appliance. Also, PBX signaling software and central office signaling require no modification for interaction according to the preferred embodiment.
In one aspect, the present invention discloses a voice network appliance. The appliance has a data connection point for connecting the appliance to a wide-area data network. It also has a signaling unit that exchanges call signaling information with one or more PBXs and one or more PSTN central offices, each having a trunk connected to the wide-area data network at a corresponding network node known to the appliance, and each connected to the appliance through a permanent virtual circuit. The appliance has a switched circuit manager to establish and manage switched virtual circuits between the nodes for the purpose of providing bearer channels for calls between the exchange and/or central office trunks connected to those nodes. A call controller controls call progression by coordinating the functions of the signaling unit and the switched circuit manager. Finally, an address translation unit receives called party addresses for call requests received by the signaling unit, determines a destination exchange and/or central office for the call requests, translates the called party addresses into formats understandable by the destination equipment, and supplies the translated addresses and destinations to the call controller.
In a further aspect of the invention, a method of operating a voice network appliance is disclosed. The method comprises connecting the voice network appliance to a node in a wide-area network, and establishing, for each of two or more wide-area network termination points, a signaling exchange wide-area network circuit between the voice network appliance and that termination point. Each termination point may terminate either a PBX trunk or PSTN trunk to a node in the wide-area network. An address translator within the appliance is provisioned to recognize, for call requests originating at each termination point, the called termination point for the called party indicated in the call request. When a call request is received from an originating termination point over its associated signaling exchange circuit, the appropriate called termination point for the called party indicated in the call request is determined, and the call request is signaled to the called termination point over its associated signaling exchange circuit. A bearer channel for the call is provided by establishing a switched virtual circuit between the originating and called termination points.